1. Field of the Invention
The invention relates to a method of fabricating semiconductor structures, and more particularly, to a method of forming zirconium oxide, hafnium oxide, composite hafnium oxide-silicon oxide and composite zirconium oxide-silicon oxide in the manufacture of an integrated circuit device.
2. Description of the Prior Art
Semiconductor devices such as field effect transistors (FET) and random access memories (RAM) are common in the microelectronics industry. Performance of a MOSFET device can be enhanced in several ways. For example, the length of the gate electrode may be reduced. Alternatively, the thickness of the gate dielectric can be reduced. Either way, the MOSFET device performs faster.
The typical material for the gate dielectric is silicon dioxide. Continued scaling of CMOS technology toward 100 nanometer and lower feature sizes has caused a progressive reduction of the gate oxide to less than 60 Angstroms. There are several negative aspects of this approach. First, silicon dioxide is facing a fundamental scaling limit due to excessive direct tunneling current. Second, there are reliability concerns due to increased charge injection. Third, gate dopants can penetrate very thin silicon dioxide. Therefore, extensive studies have been focused on developing high dielectric constant metal oxide films to replace thermal silicon dioxide.
Performance of DRAM devices is enhanced as the unit capacitance of the stacked and trench structures are increased. To achieve this, capacitors of fin, crown, and chimney shapes have been proposed. However, the fabrication of these complex structures is difficult. Hence, as in MOSFET technology, the availability of high dielectric constant metal oxide films would improve the capability of the DRAM processes.
Many high dielectric constant gate dielectrics, such as Ta2O5, BST ((Ba,Sr)TiO3), and PZT (Pb(Zr,Ti)O3), have been investigated as replacements for silicon dioxide. However, Ta2O5 has serious problems such as crystallization at about 600 degrees C. and reduction by silicon. The problem of reduction by silicon causes a shortage of oxygen atoms which lowers the withstand voltage of the film. In B. Cheng et al, xe2x80x9cThe impact of high-k gate dielectrics and metal gate electrodes on sub-100 nm MOSFET""s,xe2x80x9d IEEE Transactions on Electron Devices, Vol 46, No. 7, pp.1537-1544, it is found that BST and PZT are not only thermally unstable with a silicon substrate but also have been found to cause fringing field induced barrier lowering (FIBL). In addition, the requirement of a barrier layer between the high k dielectric and silicon further illustrates the disadvantage of these materials.
In W. Qi et al, xe2x80x9cMOSCAP and MOSFET characteristics using ZrO2 gate dielectric deposited directly on Si, IEDM Technical Digest, pp.145-148, (1999), and in B. Lee et al, xe2x80x9cUltra thin hafnium oxide with low leakage and excellent reliability for alternative gate dielectric applications,xe2x80x9d IEDM Technical Digest, pp. 133-136, (1999), it is found that zirconium oxide (ZrO2) and hafnium oxide (HfO2) show promise for future gate dielectric applications. The stability of these materials on the silicon surface and the ability to form them without the need for an interface layer, such as silicate, makes zirconium oxide and hafnium oxide good candidates to replace silicon dioxide.
Deposition of hafnium oxide and zirconium oxide is presently achieved by DC magnetron reactive sputtering or by physical vapor deposition. These methods may be suitable for blanket deposition. However, they are not suitable for difficult topologies such as the high aspect ratio trenches that are typical to DRAM and embedded DRAM technologies. The film coverage at the sidewall and bottom is insufficient using these methods. Chemical vapor deposition (CVD) at a low temperature is preferred for improving the conformal coverage of the metal oxide film. However, a new set of precursors is required.
Several prior art approaches disclose methods to form either zirconium oxide or hafnium oxide or to related technology. U.S. Pat. No. 6,020,024 to Maiti et al teaches the formation of zirconium oxide or hafnium oxide over a silicon nitride oxidation barrier. The metal oxides are formed by first sputtering the metal onto the substrate and then performing an oxidation. Alternatively, CVD may be used to deposit metal oxide followed by an oxygen anneal to reduce oxygen vacancies in the film. No details are given regarding the precursors used in CVD deposition of the metal film. U.S. Pat. No. 6,013,553 to Wallace et al teaches the formation of zirconium oxide and hafnium oxide. Hafnium or zirconium is first deposited through evaporation, sputtering, or CVD. For CVD, the precursors include hafnium tetrachloride or zirconium tetrachloride and hydrogen. Oxynitridation is achieved through direct exposure to NO or through remote plasma of nitrogen followed by oxidation. U.S. Pat. No. 5,733,661 to Ue et al teaches the formation of composite hafnium oxide and/or zirconium oxide films containing anions of organic carboxylic salts and/or inorganic oxoacid salts. The composite hafnium oxide and zirconium oxide films have relative permittivity values of between 50 and 1000, which are at least twice that of the simple oxides of hafnium and zirconium. U.S. Pat. No. 5,487,918 to Akhtar teaches the formation of hafnium oxide by reacting a hafnium substrate with hexamethyldisiloxane vapor. U.S. Pat. No. 5,443,686 to Jones et al teaches the precoating of the interior wall of a CVD reaction chamber with a thin layer of hafnium oxide or zirconium oxide, which is inert to the etching gas introduced for the removal of the silicon deposits. U.S. Pat. No. 5,405,805 to Homma teaches the exposure of zirconium oxide and hafnium oxide as insulating films in semiconductor devices to an alkoxyfluorosilane vapor to reduce water content. U.S. Pat. No. 5,405,796 to Jones, Jr. teaches the use of zirconium oxide, among other dielectric materials, as a high permittivity dielectric in the formation of a capacitor for use in a memory cell. U.S. Pat. No. 5,290,609 to Horiike et al teaches the formation of zirconium oxide or hafnium oxide as an auxiliary dielectric layer to tantalum pentoxide in a semiconductor device. Although the method of deposition of the metal oxides is CVD, no details of the precursors are given. Finally, the formation of zirconium oxide and hafnium oxide by sputtering metal followed by oxidation or by sputtering metal oxide target is practiced in the prior art.
A principal object of the present invention is to provide an effective and very manufacturable method to form high dielectric constant materials in the manufacture of an integrated circuit device.
A further object of the present invention is to provide a method to form metal oxide as a high dielectric constant material.
Another further object of the present invention is to provide a method to form composite metal oxide-silicon oxide as a high dielectric constant material.
A yet further object of the present invention is to provide precursors for the chemical vapor deposition of zirconium oxide.
Another yet further object of the present invention is to provide precursors for the chemical vapor deposition of hafnium oxide.
Another yet further object of the present invention is to provide precursors for the chemical vapor deposition of composite zirconium oxide-silicon oxide.
Another yet further object of the present invention is to provide precursors for the chemical vapor deposition of composite hafnium oxide-silicon oxide.
In accordance with the objects of this invention, a new method of forming a metal oxide high dielectric constant layer in the manufacture of an integrated circuit device has been achieved. A substrate is provided. A metal oxide layer is deposited overlying the substrate by reacting a precursor with an oxidant gas in a chemical vapor deposition chamber. The metal oxide layer may comprise hafnium oxide or zirconium oxide. The precursor may comprise metal alkoxide, metal tetraalkoxide, metal tetraalkoxide containing halogen, metal xcex2-diketonate, metal fluorinated xcex2-diketonate, metal oxoacid, metal acetate, or metal alkene. The metal oxide layer is annealed to cause densification and to complete the formation of the metal oxide dielectric layer in the manufacture of the integrated circuit device.
Also in accordance with the objects of this invention, a new method of forming a composite metal oxide-silicon oxide high dielectric constant layer in the manufacture of an integrated circuit device has been achieved. A substrate is provided. A metal oxide-silicon oxide layer is deposited overlying the substrate by reacting a precursor with an oxidant gas in a chemical vapor deposition chamber. The metal oxide-silicon oxide layer may comprise hafnium oxide-silicon oxide or zirconium oxide-silicon oxide. The precursor comprises metal tetrasiloxane. The metal oxide layer is annealed to cause densification and to complete the formation of the metal oxide-silicon oxide dielectric layer in the manufacture of the integrated circuit device.